High-co2-content natural gas crude decarburization system and process

Abstract

The application discloses a high-CO2-containing natural gas crude decarburization system and process, wherein the crude decarburization process comprises the following steps: after primary heat exchange and cooling, raw material gas is subjected to primary flash separation; after secondary heat exchange and cooling, the gas phase product obtained through the separation is subjected to secondary flash separation, thereby obtaining crude decarburization natural gas; the liquid phase products obtained through the twice flash separation are subjected to throttling refrigeration respectively, and then are reheated as heat exchange and cooling medium, and finally, CO2 is recovered through compression purification technology. The application utilizes the high pressure of the raw material gas itself to realize throttling refrigeration, and simultaneously sets two-stage flash separation devices to fully utilize the cold energy, thereby realizing low-energy-consumption and large-proportion crude decarburization, which is beneficial to further combining other processes to purify natural gas, and further greatly reducing the overall process energy consumption. In addition, the application adopts the compression purification technology to efficiently recover CO2, which is beneficial to high-value utilization and green environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of natural gas decarbonization and purification technology, and particularly relates to a crude decarbonization system and process for natural gas with high CO2 content. Background Technology

[0002] Against the backdrop of addressing global climate change, natural gas, as an important low-carbon fossil energy source, plays a particularly crucial role during the energy transition period. Due to the ongoing development of CO2 injection projects for natural gas extraction, the CO2 content in natural gas wells is gradually increasing, reaching up to 70% by volume. This makes it difficult to utilize the extracted gas as a resource, leaving a large number of high-CO2 natural gas wells undeveloped.

[0003] Natural gas contains acidic impurity gas CO2 during extraction. Its presence not only reduces the calorific value of natural gas but also corrodes pipelines, increasing transportation costs. To meet the demands of natural gas use and pipeline transportation, carbon capture technology is required to rigorously remove CO2. Conventional decarbonization technologies include membrane separation, pressure swing adsorption, amine absorption, and cryogenic methods. However, existing natural gas decarbonization technologies are not suitable for such high CO2 content conditions, facing significant challenges in terms of decarbonization energy consumption, CH4 purity, and recovery rate.

[0004] Decarbonization of high-CO2 natural gas involves a gradual transition from high-concentration CO2 decarbonization to low-concentration CO2 decarbonization, progressively purifying CH4. A single natural gas decarbonization technology struggles to simultaneously meet the requirements of energy consumption and CH4 product purity. Therefore, a combined process integrating different CO2 capture technologies is a reasonable solution to overcome these challenges, integrating the advantages of individual technologies while compensating for their shortcomings. Consequently, there is an urgent need to design a high-CO2 natural gas coarse decarbonization system and process that achieves low-energy consumption and high-proportion coarse decarbonization. Summary of the Invention

[0005] Purpose of the invention: To overcome the technical problems existing in the prior art, the present invention provides a crude decarbonization system and process for natural gas with high CO2 content. It utilizes the high-pressure throttling of the raw gas to convert it into cold energy, and then uses the cold energy to achieve gas-liquid separation, which greatly reduces the energy consumption of decarbonization. At the same time, it adopts compression purification technology to efficiently recover CO2, which is conducive to high-value utilization.

[0006] Summary of the Invention: To achieve the above objectives, the present invention provides a crude decarbonization system for natural gas with high CO2 content, comprising a primary heat exchanger, a primary flash separator, a primary throttling valve, a secondary heat exchanger, a secondary flash separator, and a secondary throttling valve;

[0007] The raw gas is cooled by heat exchange in a primary heat exchanger and then enters a primary flash separator for primary gas-liquid separation. The gaseous product obtained by separation is further cooled by heat exchange in a secondary heat exchanger and then enters a secondary flash separator for secondary gas-liquid separation, thereby obtaining crude decarbonized natural gas.

[0008] The liquid products from the primary and secondary flash separators are throttled and cooled by the primary and secondary throttle valves, respectively, and then reheated as heat exchange cooling media. Finally, CO2 is recovered through compression purification technology.

[0009] Specifically, the liquid phase product of the first-stage flash separator is throttled and cooled in the first-stage throttling valve, and then reheated as the cooling medium of the first-stage heat exchanger;

[0010] The liquid phase product of the secondary flash separator is first reheated as the cooling medium of the secondary heat exchanger, then throttled and cooled by the secondary throttling valve, and finally reheated by the secondary heat exchanger and the primary heat exchanger in sequence.

[0011] The reason why the liquid phase product of the two-stage flash separator is first used as the cooling medium of the two-stage heat exchanger for reheating, and then cooled by the two-stage throttling valve, is twofold. First, it is to make full use of the cold energy. The temperature of the liquid phase product obtained by the two-stage flash separation can reach about -54℃. The cold energy is first recovered through the two-stage heat exchanger to raise the temperature of the stream, and then the temperature of the stream is lowered by the two-stage throttling valve to further recover the cold energy. Second, it is to ensure that the temperature of the stream after throttling is higher than the triple point temperature of CO2, i.e., -56.6℃, so as to avoid CO2 condensation in the stream pipe and blockage.

[0012] Furthermore, the system also includes a compressor, a refrigeration unit, and a distillation column. The two-stage liquid products after throttling and reheating are pressurized by the compressor and then cooled and liquefied by a heat exchanger and a refrigeration unit in sequence. They then enter the distillation column for distillation and purification, thereby obtaining high-purity CO2 liquid with a CO2 volume fraction of up to 99.9%, which can be directly utilized for high-value purposes.

[0013] Furthermore, the gaseous product at the top of the distillation column is mixed with the feed gas and then recycled for decarbonization, which can further recover the natural gas component in the two-stage liquid products.

[0014] Furthermore, the gaseous products of the secondary flash separator are successively passed through a secondary heat exchanger and a primary heat exchanger to recover the cold energy, resulting in crude decarbonized natural gas.

[0015] Specifically, the feed gas is natural gas with high CO2 content after water removal and drying, wherein the volume fraction of CO2 is higher than 50%.

[0016] Specifically, the CO2 volume fraction in the crudely decarbonized natural gas is less than 28%, thereby achieving the goal of high-proportion crude decarbonization and effectively reducing the power consumption of the subsequent CH4 purification process.

[0017] In addition, the present invention also provides a crude decarbonization process for natural gas with high CO2 content, comprising the following steps:

[0018] The feed gas undergoes a flash separation after a heat exchange and cooling process. The resulting gaseous product undergoes a second flash separation after a second heat exchange and cooling process, thereby obtaining crude decarbonized natural gas.

[0019] The liquid products obtained from the two flash evaporation separations were subjected to throttling refrigeration, then reheated as heat exchange cooling media, and finally recovered by compression purification technology.

[0020] Specifically, the liquid product obtained from the first flash separation is reheated as a heat exchange cooling medium after being throttled and cooled.

[0021] The liquid product obtained from the secondary flash evaporation separation is first reheated as a secondary heat exchange cooling medium, then subjected to throttling cooling, and finally reheated as both a secondary and primary heat exchange cooling medium.

[0022] Specifically, the liquid phase products obtained from the two flash evaporation separations are first pressurized and liquefied after throttling and reheating, and then purified by distillation to obtain high-purity CO2 liquid. The gas phase products obtained from the distillation purification are mixed with the raw gas and then recycled for decarbonization.

[0023] Beneficial Effects: This invention utilizes the high pressure of the raw gas itself to achieve throttling and refrigeration, while incorporating a two-stage flash separation device to fully utilize the cooling capacity, thereby achieving low-energy, high-proportion coarse decarbonization. Based on the concept of staged decarbonization, this invention, while achieving low-energy, high-proportion coarse decarbonization, further combines it with other processes for natural gas purification, significantly reducing overall process energy consumption. Furthermore, this invention employs compression purification technology for efficient CO2 recovery, facilitating high-value utilization, and is environmentally friendly, energy-efficient, and highly effective. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the process of the high CO2 content natural gas crude decarbonization system in an embodiment of the present invention;

[0025] The diagram includes: 1. Primary flash separator, 2. Primary throttling valve, 3. Primary heat exchanger, 4. Secondary heat exchanger, 5. Secondary flash separator, 6. Secondary throttling valve, 7. Compressor, 8. Refrigeration unit, and 9. Distillation column. Detailed Implementation

[0026] To make the technical solutions of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Reference Figure 1 This embodiment provides a crude decarbonization system for natural gas with high CO2 content, including a primary heat exchanger 3, a primary flash separator 1, a primary throttling valve 2, a secondary heat exchanger 4, a secondary flash separator 5, a secondary throttling valve 6, a compressor 7, a refrigeration unit 8, and a distillation column 9;

[0028] In this process, the raw gas is mixed with the gaseous reflux product at the top of the distillation column 9, and after being cooled by the first-stage heat exchanger 3, it enters the first-stage flash separator 1 for a first gas-liquid separation. The top gaseous product obtained by the separation is further cooled by the second-stage heat exchanger 4 and then enters the second-stage flash separator 5 for a second gas-liquid separation, thereby obtaining crude decarbonized natural gas.

[0029] The bottom liquid product of the first-stage flash separator 1 is throttled and cooled in the first-stage throttling valve 2, and then reheated as the cooling medium of the first-stage heat exchanger 3; the bottom liquid product of the second-stage flash separator 5 is first reheated as the cooling medium of the second-stage heat exchanger 4, then throttled and cooled by the second-stage throttling valve 6, and finally reheated by the second-stage heat exchanger 4 and the first-stage heat exchanger 3 in sequence.

[0030] After throttling and reheating, the two-stage liquid products are pressurized by compressor 7 and then cooled and liquefied by first-stage heat exchanger 3 and refrigeration unit 8. They then enter distillation column 9 for distillation and purification. High-purity CO2 liquid product is obtained from the bottom outlet of distillation column 9, while the gaseous product at the top of distillation column 9 is mixed with the raw gas and then recycled for decarbonization.

[0031] Specifically, the feed gas is high-CO2 natural gas after water removal and drying, with a CO2 volume fraction >50%. Based on the inherent properties of the gas well, the feed gas itself carries a high pressure (above 3 MPa, reaching tens of megapascals). Therefore, this invention creatively utilizes the high pressure of the feed gas itself to achieve throttling refrigeration, employing a two-stage throttling valve to generate cooling capacity, thereby meeting heat exchange requirements. To prevent CO2 condensation and blockage in the flow pipes, the flow temperature after throttling by the two-stage valves should be higher than the triple point temperature of CO2, i.e., -56.6℃. Based on this, the first and second stage flash temperatures are rationally set. Generally, the first-stage flash temperature can reach approximately -25℃, and the second-stage flash temperature can reach approximately -54℃, thus achieving CO2 liquefaction and separation through two heat exchange cooling processes.

[0032] Specifically, both the primary heat exchanger 3 and the secondary heat exchanger 4 are multi-stream heat exchangers to fully utilize the cooling capacity generated by high-pressure throttling. If the inlet flow pressure of the compressor 7 is different, two compressors 7 can be installed, with the flow streams undergoing high and low-pressure compression respectively before merging. Alternatively, a single intermediate-pressure compressor 7 can be installed. The process combines throttling refrigeration and ammonia refrigeration to liquefy the raw material gas, which is then preliminarily separated by flash evaporation before being purified by distillation to ensure the purity of the CO2 liquid product. The top of the distillation column 9 does not have a condenser, but a reboiler is installed at the bottom to ensure that high-purity CO2 liquid product is discharged from the bottom outlet of the distillation column 9, with a CO2 volume fraction of up to 99.9%, which can be directly utilized for high-value purposes.

[0033] Furthermore, the top gaseous product of the secondary flash separator 5 is passed through the secondary heat exchanger 4 and the primary heat exchanger 3 to recover the cold energy, thereby obtaining a crude decarbonized natural gas product with a CO2 volume fraction of 23% to 26%, so as to maintain a stable CO2 concentration in the crude decarbonized natural gas product and reduce the impact on the subsequent CH4 purification process.

[0034] In addition, this embodiment also provides a crude decarbonization process for natural gas with high CO2 content, specifically including:

[0035] The feed gas undergoes a flash separation after a heat exchange and cooling process. The resulting gaseous product undergoes a second flash separation after a second heat exchange and cooling process, thereby obtaining crude decarbonized natural gas.

[0036] The liquid phase product obtained from the first flash separation is reheated as the primary heat exchange cooling medium after throttling cooling; the liquid phase product obtained from the second flash separation is first reheated as the secondary heat exchange cooling medium, then throttled cooling, and finally reheated as the secondary heat exchange cooling medium and the primary heat exchange cooling medium in sequence.

[0037] The liquid products obtained from the two flash evaporation separations are first pressurized and liquefied after throttling and reheating, and then purified by distillation to obtain high-purity CO2 liquid. The gaseous products obtained from the distillation purification are mixed with the raw gas and then recycled for decarbonization.

[0038] After the feed gas undergoes a crude decarbonization process for high-CO2 natural gas, it can be combined with other CH4 purification processes, such as amine absorption, pressure swing adsorption, and membrane separation, to further achieve decarbonization of low-concentration CO2 natural gas. Taking this process combined with amine absorption decarbonization as an example, when the CO2 concentration of the feed gas is 70%, the crude decarbonization process can account for 87% of the total decarbonization, while the decarbonization energy consumption of the traditional amine absorption method can reach 300 kWh / t CO2. Since the purification process only accounts for 13% of the total decarbonization, the overall combined decarbonization process energy consumption can be reduced to 120 kWh / t CO2. Compared with the amine absorption process alone, the combined decarbonization process can significantly reduce the overall energy consumption.

[0039] The following examples use three different concentrations of high CO2 (>50%) natural gas for experimental simulation. The composition and content of the simulated feed gas are shown in Table 1. Mechanical losses and pipeline pressure losses in the experiment are negligible. The adiabatic efficiency of equipment such as the compressor is 0.85, the pressure drop in the distillation column is calculated as 2 kPa, and the heat exchanger channel resistance is calculated as 1 kPa. Referring to actual engineering practices, the temperature difference at the heat exchanger ends of the refrigeration unit is taken as 10℃, the minimum temperature difference at the heat exchanger ends as 1.5℃, the temperature difference at the interstage cooler ends of the compressor as 5℃, and the cooling circulating water temperature as 30–40℃.

[0040] Table 1. Components and content of simulated feed gas

[0041]

[0042] Example 1:

[0043] Simulations were performed using the Aspen Plus system. The CO2 volume fraction in the feed gas was 50%, and the pressure of the feed gas after dehydration and drying was 3 MPa. The main production indicators are as follows:

[0044] Roughly stripped natural gas stream:

[0045] Ingredients: CO2: 23.89%, CH4: 75.73%, C2H4: 0.227%, N2: 0.154%;

[0046] Temperature: 10℃;

[0047] CH4 recovery rate: 99.99%;

[0048] Product CO2 stream:

[0049] Ingredients: CO2: 99.9%, CH4: 0.0008%, C2H4: 0.149%, N2: 0%;

[0050] Pressure: 30 bar;

[0051] Temperature: -5.4℃;

[0052] Liquid CO2 product mass flow rate: 12.16 t / h;

[0053] Liquid CO2 product purity: 99.9%;

[0054] Crude CO2 removal ratio: 70%;

[0055] Energy consumption of the refrigeration unit: 520.2kW;

[0056] Compressor energy consumption: 646.6kW;

[0057] Cooling water consumption: 2111.9 t / h;

[0058] System unit energy consumption (calculated based on CO2 in the product): 103.9 kWh / t CO2.

[0059] Example 2:

[0060] Simulations were performed using the Aspen Plus system. The CO2 volume fraction in the feed gas was 70%, and the pressure of the feed gas after dehydration and drying was 3 MPa. The main production indicators are as follows:

[0061] Roughly stripped natural gas stream:

[0062] Ingredients: CO2: 23.88%, CH4: 75.58%, C2H4: 0.284%, N2: 0.259%;

[0063] Temperature: 10℃;

[0064] CH4 recovery rate: 99.99%;

[0065] Product CO2 stream:

[0066] Ingredients: CO2: 99.9%, CH4: 0.003%, C2H4: 0.147%, N2: 0%;

[0067] Pressure: 30 bar;

[0068] Temperature: -5.3℃;

[0069] Liquid CO2 product mass flow rate: 21.30 t / h;

[0070] Liquid CO2 product purity: 99.9%;

[0071] CO2 removal rate: 87%;

[0072] Energy consumption of the refrigeration unit: 910.3kW;

[0073] Compressor energy consumption: 947.9kW;

[0074] Cooling water consumption: 352.8 t / h;

[0075] System unit energy consumption (calculated based on CO2 in the product): 96.1 kWh / t CO2.

[0076] Example 3:

[0077] Simulations were performed using the Aspen Plus system. The CO2 volume fraction in the feed gas was 80%, and the pressure of the feed gas after dehydration and drying was 3 MPa. The main production indicators are as follows:

[0078] Roughly stripped natural gas stream:

[0079] Ingredients: CO2: 23.87%, CH4: 75.40%, C2H4: 0.347%, N2: 0.393%;

[0080] Temperature: 10℃;

[0081] CH4 recovery rate: 99.99%;

[0082] Product CO2 stream:

[0083] Ingredients: CO2: 99.9%, CH4: 0.003%, C2H4: 0.150%, N2: 0%;

[0084] Pressure: 30 bar;

[0085] Temperature: -5.3℃;

[0086] Liquid CO2 product mass flow rate: 25.86 t / h;

[0087] Liquid CO2 product purity: 99.9%;

[0088] CO2 removal rate: 93%;

[0089] Energy consumption of the refrigeration unit: 1164.2kW;

[0090] Compressor energy consumption: 1178.7kW;

[0091] Cooling water consumption: 450.3 t / h;

[0092] System unit energy consumption (calculated based on CO2 in the product): 101.9 kWh / t CO2.

[0093] As demonstrated by the above examples, this process can achieve high-ratio decarbonization with low energy consumption for feed gases of varying CO2 concentrations. High-pressure throttling and refrigeration of the feed gas effectively reduces decarbonization energy consumption. Furthermore, the CO2 removal rate can reach up to 90%, yielding a 99.9% pure liquid CO2 product that can be directly utilized for high-value applications. In summary, this combined decarbonization process based on the coarse decarbonization technique significantly reduces overall decarbonization energy consumption compared to a single process.

[0094] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A crude decarbonization system for high CO2-content natural gas, characterized in that, It includes a primary heat exchanger, a primary flash separator, a primary throttling valve, a secondary heat exchanger, a secondary flash separator, and a secondary throttling valve; The feed gas is a dehydrated and dried gas containing CH4 and C2H4 hydrocarbon components. After being cooled by heat exchange in a primary heat exchanger, it enters a primary flash separator for primary gas-liquid separation. The separated gaseous products are further cooled by heat exchange in a secondary heat exchanger and then enter a secondary flash separator for secondary gas-liquid separation, thereby obtaining crude decarbonized natural gas. The liquid products of the first-stage flash separator and the second-stage flash separator are throttled and cooled by the first-stage throttle valve and the second-stage throttle valve, respectively, and then reheated as heat exchange cooling media. Finally, CO2 is recovered through compression purification technology. The liquid products of the first-stage flash separator are throttled and cooled by the first-stage throttle valve and are only used as cooling media for the first-stage heat exchanger for reheating, and do not enter the second-stage heat exchanger.

2. The high-CO2-content natural gas crude decarbonization system according to claim 1, characterized in that, The liquid phase product of the first-stage flash separator is throttled and cooled in the first-stage throttling valve, and then reheated as the cooling medium of the first-stage heat exchanger. The liquid phase product of the secondary flash separator is first used as the cooling medium of the secondary heat exchanger for reheating, and then throttled and cooled by the secondary throttling valve. After cooling, the temperature is higher than the triple point temperature of CO2 by 56.6℃. Finally, it is reheated by the secondary heat exchanger and the primary heat exchanger in sequence.

3. The high CO2 content natural gas crude decarbonization system according to claim 1, characterized in that, It also includes a compressor, a refrigeration unit, and a distillation column. The two-stage liquid products after throttling and reheating are pressurized by the compressor, then cooled and liquefied by a heat exchanger and a refrigeration unit, and then enter the distillation column for distillation and purification to obtain high-purity CO2 liquid.

4. The high CO2 content natural gas crude decarbonization system according to claim 3, characterized in that, The gaseous products at the top of the distillation column are mixed with the feed gas and then recycled for decarbonization.

5. The high CO2 content natural gas crude decarbonization system according to claim 1, characterized in that, The gaseous products of the secondary flash separator are sequentially passed through a secondary heat exchanger and a primary heat exchanger to recover their cooling capacity, resulting in crude decarbonized natural gas.

6. The high CO2 content natural gas crude decarbonization system according to claim 1, characterized in that, The feed gas is natural gas with high CO2 content after water removal and drying, wherein the volume fraction of CO2 is higher than 50%.

7. The high CO2 content natural gas crude decarbonization system according to claim 1, characterized in that, The CO2 volume fraction in the crudely decarbonized natural gas is less than 28%.

8. A process implemented using the high CO2 content natural gas crude decarbonization system as described in any one of claims 1-7, characterized in that, Includes the following steps: The feed gas containing CH4 and C2H4 hydrocarbons is subjected to flash separation after one heat exchange cooling. The separated gaseous products are subjected to flash separation after a second heat exchange cooling, thereby obtaining crude decarbonized natural gas. The liquid products obtained from the two flash evaporation separations were subjected to throttling refrigeration, then reheated as heat exchange cooling media, and finally recovered by compression purification technology.

9. The process according to claim 8, characterized in that, The liquid product obtained from the first flash separation is reheated as the primary heat exchange cooling medium after throttling and cooling, and this liquid product does not enter the secondary heat exchange process; the liquid product obtained from the second flash separation is first reheated as the secondary heat exchange cooling medium, then throttled and cooled, and the temperature after cooling is higher than the triple point temperature of CO2 -56.6℃, and finally reheated as the secondary heat exchange cooling medium and the primary heat exchange cooling medium in sequence.

10. The process according to claim 8, characterized in that, The liquid products obtained from the two flash evaporation separations are first pressurized and liquefied after throttling and reheating, and then purified by distillation to obtain high-purity CO2 liquid. The gaseous products obtained from the distillation purification are mixed with the raw gas and then recycled for decarbonization.

Images